Odd misfire at idle on 5.3

[Chad G 1979]

Is this when the engine is warmed up and idling between 500 and 600 rpms? A slight shudder? I notice it on occasion when waiting for my kiddos from school and my tahoe is idlong and warmed up. I dont hear any odd idling sound or misfiring, just has an odd shudder. I did notice that it likes to idle at around 500ish rpm on the tach so maybe its idle rpms is a bit low? If i put just a bit of throttle response and get rpms to over 600 it goes away. Just my observation from what i see in my ride.

 

[TexasLC]

it happens at idle yes with a warm engine. I've never seen the tach needle move when it occurs. It will happen for about 1-2 seconds. Long enough to notice and look at the dash, and then it's over. No lights, no needle movement. But you know the shuddering happened and it sounded like the motor was choking and going to die or something. or misfiring and then the computer maybe recalibrates or something. It never happens long enough to be able to think to push the throttle and rev it out of idle.

 

[Matahoe]

Exactly right. No lights, no warnings, no rpm tach bouncing.

I thought about gas possibly too but it’s too infrequent I think. I run 87 also. And it never happens when the motor is moving through a rev range.

Given the year of your vehicle I would start simple. Always start with simplest repair first. I would run a few bottles of fuel system cleaner like Berrymans B-12 Chemtool. It solved my intermittent rough idle. Sounds like leaking injector(s). Now the reason it runs fine off idle is because higher rpm masks a rich idle condition which a leaking injector would cause.

Don't be afraid to give it a bit of an Italian tuneup after the cleaner has worked it's way through. Couple weeks or so, dep on how much you drive. In the mean time you can flush and change the oil with 5w-20, clean MAF and check fuel pressure at rail valve.

 

[WalleyeMikeIII]

I would start with a few bottles of some fuel system cleaner like Berrymans B-12 Chemtool. It solved my intermittent rough idle. Sounds like leaking injector(s). Sure it's possible it runs fine off idle because higher rpm masks a rich idle condition which a stuck injector would cause.

I would recommend using GM's branded fuel system cleaner, esp if you are in warranty, so there are no "issues" about things later. It's pretty near the same money at the dealer (really I think it is just Chevron Techron), but....

 

[Matahoe]

Proper use of reputable fuel and oil additives does not void car warranties. Consumer protection is afforded by the Magnuson-Moss Warranty Act.

 

[Innovatah]

I have my truck 2008 yukon in the shop for this exact reason but waiting to see their response. I thought maybe it was engine mount but it's not. Only happened twice so far. No check engine light or anything. Did anyone find what the issue was/is?

 

[robnarley]

Could be a manifold absolute pressure (MAP) sensor issue. At idle the ECM uses the input from this sensor, but any time there is throttle input, the airflow to the engine increases and the ECM uses the input from the mass airflow (MAF). I had this issue and the problem was intermittent and progressively got worse. When the sensor was acting up, the idle was VERY rough. However, if it was only for a second or two, it wouldn’t throw any codes. If it lasted longer than a couple seconds, it would throw a random misfire code. This was on a 2006 Sierra 5.3. A newer vehicle might have the capability of throwing a MAP sensor specific code.

 

[B520044]

I just had my oil changed yesterday, along with 2 recalls completed. Shortly after dropping off my vehicle they called to say they recommend a throttle body cleaning and cabin filter replacement. I turned them down, as I can easily perform the filter replacement myself. However, I found it odd that they asked about the throttle body cleaning?? Has anyone else been told this was recommended? I only have 26k miles on my AT4. Could throttle body cleaning help a ruff idle?

 

[Matahoe]

I wouldn't think your throttle body would be dirty much at your mileage. Has there been anything aftermarket added like a K&N air filter or any maintenance under the hood since 0 on the odometer? A bit of back story helps.

 

[TexasLC]

I wouldn't think your throttle body would be dirty much at your mileage. Has there been anything aftermarket added like a K&N air filter or any maintenance under the hood since 0 on the odometer? A bit of back story helps.

Car has 30,000 miles and zero mods or anything. It’s been random moments when it happened. No rhyme or reason or pattern to discern. Just last maybe .5-2 seconds at most and not to be seen or heard from again for days or weeks at a time. Even a month will pass.